Smelly Basement? Just Add Water.

If you notice a foul sewer smell in your basement, the mostly likely culprit is an empty water trap. How do you fix it? Just pour a gallon of water into the basement floor drain.

It’s that simple, but for those who want to know why this works, I’ll explain how a water trap works, how to keep that smell from coming back later, and how you can use this trick in other parts of your house.

How a Water Trap Works

That drain in your basement floor leads to a U-bend, and that U-bend contains water. Aka, a “water trap.” This water acts as a seal, keeping the foul smells from wafting up the pipe, through the drain, and into your basement.

However, water in any trap under unused drains will eventually evaporate. When it all evaporates, sewer gas comes up through the drain into the room. Pour a pitcherful of water into the drain to restore the trap water. The water will collect in the U-bend and create a new seal.

How to Keep the Smell from Coming Back

You can greatly slow how quickly trap water evaporates by adding a teaspoon of vegetable oil. The oil will rise to the top and spread out in a thin layer to cover the surface of the water. This thin cover will slow the water’s evaporation rate.

How to Use This Trick Throughout Your House

Water traps exist throughout your house. If you look underneath your sink, for instance, you’ll see a U-bend—that’s a water trap. Many people think these bends are meant to keep things you drop in the sink from going all the way out the pipe. They do accomplish that, but any U-bend/water trap is primarily designed to be a seal that keeps gasses from coming up the pipe into your home.

You can find water traps beneath showers, sinks, and toilets. If any of those go unused for long periods of time, you might need to replenish the water trap.